Electron hydrodynamics - microscopic origins and effects of nanoscale geometries

Electrons in condensed matter can flow collectively when their momentum is conserved during microscopic scattering processes. Recently, this hydrodynamic regime has been observed in a handful of materials classes at moderately low temperatures and small lengthscales.^1-2 The reason for this narrow temperature/lengthscale regime is the competition between the ballistic (low temperatures/small lengthscales) and diffusive (high temperatures/large lengthscales) regimes.

In this work, we compute temperature-resolved viscosity tensors for a broad range of materials from first principles and identify diagnostic tools for hydrodynamic behavior from microscopic scattering lifetimes. We then investigate the effect of nanoscale geometries on these viscous electron fluids, by comparing the results of the electronic Navier stokes equation with ab-initio viscosity tensors,³ to an independent calculation of the spatially-resolved Boltzmann transport equation using the same ab-initio scattering matrix.<sup>4

1</sup> Sulpizio, J. A. et al. Nature 576, 75–79 (2019).
² Vool, U., Hamo, A., Varnavides, G., Yaxian, W. et al arXiv:2009.04477 (2020)
³ Varnavides, G., Jermyn, A.S., Anikeeva, P. et al. Nat Commun 11, 4710 (2020)
⁴ Varnavides G., Jermyn A.S., Anikeeva P. et al. Phys. Rev. B 100 115402 (2019)